Computational Fluid Dynamics and Airplane Design: Its Current and Future Impact

140 Pages·2008·22.94 MB·English

by  Antony Jameson

Computational Fluid Dynamics
and Airplane Design:
Its Current and Future Impact
Antony Jameson1
1ThomasV.JonesProfessorofEngineering
Department ofAeronautics &Astronautics
StanfordUniversity
AssistedbyNaweeButsuntorn
withContributionsfromNASA:
SusanCliff
Boeing:
DouglasBall,EdTinoco
andDLR/Airbus:
NorbertKroll,CordRossow,KlausBecker
University of Cincinnati
February 22, 2008
1 Elements of Aerodynamic Design
Tradeoffs
Design Process
2 Impact of CFD on Airplane Design
Emergence of CFD 1965–2005
Boeing
DLR & Airbus
3 Future Impact
Optimization
Shock free airfoils
Super B747
Flight at Mach 1
Reduced Sweep
ElementsofAerodynamicDesign
ImpactofCFDonAirplaneDesign
FutureImpact
Elements of Aerodynamic Design
AntonyJameson CFDandAirplaneDesign:ItsCurrentandFutureImpact
ElementsofAerodynamicDesign
Tradeoffs
ImpactofCFDonAirplaneDesign
DesignProcess
FutureImpact
Aerodynamic Design Tradeoffs
A good first estimate of performance is provided by the Breguet range
equation:
VL 1 W0+Wf
Range= log . (1)
D SFC W
0
Here V is the speed, L/D is the lift to drag ratio, SFC is the specific fuel
consumption of the engines, W is the loading weight (empty weight +
0
payload + fuel resourced), and Wf is the weight of fuel burnt.
Equation (1) displays the multidisciplinary nature of design.
A light structure is needed to reduce W . SFC is the province of the
0
engine manufacturers. The aerodynamic designer should try to maximize
VL. This means the cruising speed V should be increased until the onset
D
of drag rise at a Mach Number M = V .85. But the designer must
C
∼
also consider the impact of shape modifications in structure weight.
AntonyJameson CFDandAirplaneDesign:ItsCurrentandFutureImpact
ElementsofAerodynamicDesign
Tradeoffs
ImpactofCFDonAirplaneDesign
DesignProcess
FutureImpact
Aerodynamic Efficiency of Long Range Transport Aircraft
Variation of L/D vs. M Variation of M L/D vs. M
20 20
18
18
16
16 14
14 12
L/D M L/D10
12 8
10 6
4
8
2
60 0.5 1 1.5 2 00 0.5 1 1.5 2
M M
AntonyJameson CFDandAirplaneDesign:ItsCurrentandFutureImpact
ElementsofAerodynamicDesign
Tradeoffs
ImpactofCFDonAirplaneDesign
DesignProcess
FutureImpact
Aerodynamic Design Tradeoffs
The drag coefficient can be split intoan approximatefixed component CD ,
0
and theinduced drag dueto lift.
C
CD =CD + L2 (2)
0 πǫAR
where AR is theaspect ratio, and ǫ is an efficiency factor close to unity. CD
0
includes contributions such as friction and form drag. It can beseen from this
equation that L/D is maximized by flying at a lift coefficient such thatthetwo
terms are equal, so that theinduced drag is half thetotal drag. Moreover, the
actualdrag dueto lift
2L2
Dv =
πǫρV2b2
varies inversely with thesquareof thespan b. Thusthere is a direct conflict
between reducingthe dragby increasing thespan and reducing thestructure
weight by decreasing it.
AntonyJameson CFDandAirplaneDesign:ItsCurrentandFutureImpact
ElementsofAerodynamicDesign
Tradeoffs
ImpactofCFDonAirplaneDesign
DesignProcess
FutureImpact
Weight Tradeoffs
σt
d
a
The bendingmoment M is carried largely by theupperand lower skin of the
wing structurebox. Thus
M =σtda
For a given stress σ, therequired skin thickness varies inversely as thewing
depth d. Thus weight can be reduced by increasing thethickness to chord
ratio. But thiswill increase shock drag in thetransonic region.
AntonyJameson CFDandAirplaneDesign:ItsCurrentandFutureImpact
ElementsofAerodynamicDesign
Tradeoffs
ImpactofCFDonAirplaneDesign
DesignProcess
FutureImpact
Overall Design Process
Defines Mission
15−30 engineers Conceptual
Preliminary sizing
1.5 years Design
Weight, performance
$6−12 million
100−300 engineers
Preliminary
2.5 years
$60−120 million Design
6000 engineers
5 years Final Design
$3−12 billion
AntonyJameson CFDandAirplaneDesign:ItsCurrentandFutureImpact
ElementsofAerodynamicDesign
Tradeoffs
ImpactofCFDonAirplaneDesign
DesignProcess
FutureImpact
Cash Flow
Economic Projection (Jumbo Jet)
Cash Flow
$ billion Conceptual Design
Decisions here decide
final cost and performance
Preliminary Design Leads to performance guarantees
−300 m
1.5 4 9 15 Year
−2 Detailed Design 400 aircraft
−4 and certification 80 b sales
−6
Launch
−8
(if atleast 100 orders)
−10
−12
−12 b
AntonyJameson CFDandAirplaneDesign:ItsCurrentandFutureImpact
ElementsofAerodynamicDesign
Tradeoffs
ImpactofCFDonAirplaneDesign
DesignProcess
FutureImpact
Aerodynamic Design
AntonyJameson CFDandAirplaneDesign:ItsCurrentandFutureImpact